Carbon elimination and cooling improvement to scroll type combustors

ABSTRACT

AN IMPROVEMENT FOR APPARATUS OF THE TYPE ADAPTED TO PREMIX AIR AND FUEL OR CARBURET AIR PRIOR TO INTRODUCTION THEREOF AS A VORTICAL FLOW INTO A PRIMARY ZONE OF A COMBUSTOR, THE IMPROVEMENT COMPRISES A PURGE AIR OPENING POSITIONED WITHIN AN UPSTREAM WALL OF A SPIN CHAMBER AND COVERED BY A CAP HAVING A PLURALITY OF SMALL OPENINGS LOCATED THEREIN. PURGE AIR FLOWS FROM THE COMPRESSOR THROUGH THE SMALL OPENINGS INTO A CHAMBER FORMED BY THE CAP AND THEREAFTER INTO THE SPIN CHAMBER IN SUCH A MANNER AS TO PREVENT IMPINGEMENT OF HIGH TEMPERATURE GASES ON THE UPSTREAM WALL OF THE SPIN CHAMBER WITHOUT DETRIMENTALLY AFFECTING GENERATION OF THE PRIMARY VORTICAL FLOW.

Sept. 20, 1971 3,605,405

T. L. DU ELL CARBON ELIMINATION AND COOLING IMPROVEMENT T0 SCROLL TYPEcomaus'rons Filed April 9, 1970 2 Sheets-Sheet 1 42"4 I g /Q jINVENTORS. THOMAS L. Du BELL BY BARRY WEINSTEIN AGINT- Sept. 20, 1971'r. L. DU BELL 3,605,405

CARBON ELIMINATION AND COOLING IMPROVEMENT TO SCROLL TYPE COMBUS'I'ORSFiled April 9, 1970 2 Sheets-Sheet 2 INVEN'T R5 THOMAS L. DU ELL BYBARRY WE|N$TEIN AQINY- United States Patent O US. Cl. 6039.65 11 ClaimsABSTRACT OF THE DISCLOSURE An improvement for apparatus of the typeadapted to premix air and fuel or carburet air prior to introductionthereof as a vortical flow into a primary zone of a combustor; theimprovement comprises a purge air opening positioned within an upstreamwall of a spin chamber and covered by a cap having a plurality of smallopenings located therein. Purge air flows from the compressor throughthe small openings into a chamber formed by the cap and thereafter intothe spin chamber in such a manner as to prevent impingement of hightemperature gases on the upstream wall of the spin chamber withoutdetrimentally affecting generation of the primary vortical flow.

BACKGROUND OF THE INVENTION This invention relates generally tocombustion apparatus for supplying fuel to a combustion chamber. Moreparticularly, this invention relates to improvements in the above typeapparatus which eliminate carbon accumulation and overtemperatureproblems presently associated therewith.

The invention herein described was made in the course of or under acontract, or a subcontract thereunder, with the United States Departmentof the Air Force.

Delivery of fuel into a continuous burning combustion apparatus, as forexample in gas turbine engine combustors, in a highly dispersed mannerso as to achieve complete and efiicient combustion of the fuel and, atthe same time, minimize the occurrence of fuel-rich pockets, which uponcombustion produce carbon or smoke, has posed a continuing problem togas turbine engine manufacturers. Solutions to this problem are furthercomplicated in applications such as gas turbine engines by the hightemperature environment of the combustion chamber as well as by overalllength and weight limitations for such combustion apparatus.

Present day emphasis on the elimination of air pollution has resulted ina great deal of work and effort by gas turbine engine manufacturers inan attempt to eliminate visible smoke emission from gas turbine engines.One proposed solution to the foregoing problems involves the use of adevice for carbureting the inlet air or mixing the air and fuel and fordelivering the combustible fuel/air mixture into the primary zone of acombustor as a vortical flow. Such an apparatus is shown and claimed ina copending application of Thomas L. Du Bell, Ser. No. 817,075, entitledFuel Delivery Apparatus, and assigned to the same assignee as thepresent application. The apparatus comprises a housing defining an airvortex generator or spin chamber therein about a centrally disposed coreoutlet. The housing is adapted to receive fuel and air, circulate thefuel and air through an array of swirl vanes in the spin chamber andgenerate a vortical discharge flow of air and highly dispersed fuel. Theapparatus may include a collection surface provided at the core outletfor collection of non-vaporized or atomized fuel that may be expelledfrom the apparatus. A secondary array of swirl vanes surrounds thecollection surface in such a manner as to generate and deliver asecondary vortical flow into the combustion chamber, about the primaryice vortex, which is generally coaxial with and counterrotating relativeto the primary vortex.

Such an apparatus has been found to produce an extremely well vaporizedfuel/air mixture with a resultant high efficiency and a reduction insmoke emission from the combustion apparatus. Certain applications ofsuch an apparatus, however, have been found to result in carbonaccumulation and metal overtemperatures such that normal operation, asdescribed above, could be detrimentally affected.

Previous attempts to solve similar problems in such apparatus have beento ventilate the affected area by perforating the metal, therebyallowing copious amounts of air to flow through at very high velocities.Such an approach, however, frequently destroys the basic aerodynamics ofthe apparatus 'by upsetting the vortex previously generated. The netresult is a worsening of ignition capability and poorer fueldistribution, which, in turn, results in poorer eXit temperaturedistributions.

Accordingly, a primary object of this invention is to provide animproved scroll cup type fuel vaporizer which prevents carbonaccumulation and metal overtemperature Without affecting the vortex flowthereof.

Another object of this invention is to provide an improved apparatus asdescribed above which controls the recirculation of gases into thecenter of the primary vortex.

SUMMARY OF THE INVENTION Briefly stated, the above and other objects areachieved in the present invention by providing a basic scroll housingwith an opening in a generally planar upstream wall which forms one endof a spin chamber adapted to receive and circulate pressurized air andfuel around a central or core outlet in flow communication with thecombustion chamber. A pan-shaped member is attached to the upstream wallof the scroll cup in such a manner as to surround the opening therein.The pan-shaped member is provided with a plurality of small openings inone face thereof, which openings may be normal to or inclined withrespect to the surface of the pan-shaped member. The openings arepositioned to prevent direct axial flow through the opening in theupstream wall of the scroll cup and they are sized so as to provide alow velocity flow of purge air through the opening in the upstream wallmember to the spin chamber of the scroll cup. In this manner,recirculating hot gases within the vortex are prevented from impingingupon the interior walls of the scroll cup.

DESCRIPTION OF THE DRAWINGS While the specification concludes withclaims particularly pointing out and distinctly claiming the subjectmatter of this invention, it is believed that the invention will bebetter understood upon reading the following description of a preferredembodiment in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary axial cross-sectional view of an exemplary gasturbine engine combustion apparatus embodying the improved scroll cupapparatus of this invention;

FIG. 2 is a perspective view, with portions removed, of the improvedapparatus of FIG. 1;

FIG. 3 is a diagrammatical axial cross-sectional view of a scroll cupapparatus without the present improvement showing the air and fuel flowpatterns generated thereby;

FIG. 4 is a diagrammatical axial cross-sectional view of the apparatusof FIG. 2 showing the improved air and fuel flow patterns generatedthereby; and

FIG. 5 is a front end view of the improved apparatus of FIG. 1.

3 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to thedrawings wherein like numerals correspond to like elements throughout,attention is drawn to FIG. 1 wherein a continuous burning combustionapparatus of a type suitable for use in a gas turbine engine has beenshown generally at as comprising a hollow body 12 defining a combustionchamber 14 therein. The hollow body 12 includes a domed upstream closuremember 16, having an opening 18 located centrally thereof for receivinga fuel/ air mixture. The domed closure member 16 defines the upstreamend of the combustion chamber 14 and may be suitably secured to orformed integrally with the hollow body 12. As will be understood bythose skilled in the art, the combustion chamber 14 may be of theannular type, the cannular type, or the can type, with the domed closuremember 16 having a plurality of circumferentially spaced openings 18.

An outer shell 20 may be provided to enclose the hollow body 12 and tocooperate therewith to form passageways 22 and 24 surrounding the hollowbody '12. An upstream extension 26 of the hollow body 12 cooperates withthe outer shell 20 to form the inlets of the passageways 22 and 24. Aswill be understood, the passageways 22 and 24 are adapted to deliver aflow of pressurized air from a suitable source, such as a compressor 28,into the combustion chamber 14 through suitable apertures or louvers 30.In this manner, the passageways 22 and 24 act to both cool the hollowbody 12 and to provide dilution air to the gaseous products ofcombustion formed within the combustion chamber 14.

The upstream extension 26 of hollow body 12 is adapted to function as aflow splitter to divide the pressurized air delivered from thecompressor 28 between the passageways 22 and 24 and an upstream endopening 32 centrally formed within the extension 26. As clearly shown inFIG. 1, the opening 32 communicates with a chamber 33, which is definedby the internal wall of the extension 26 and the external wall of thedomed member 16.

Located within the chamber 33 and attached to the domed member 16 in anysuitable manner known in the art is an improved fuel injection apparatus34 constructed in accordance with this invention. The fuel injectionapparatus 34 has been shown as comprising a housing 35 having inletpassage means 36 for receiving pressurized air from the compressor 28 bymeans of the opening 32, a first or core outlet 38 (FIG. 2) in fiowcommunication with the hollow body opening 18 for delivery of an air/fuel mixture into the combustion chamber 14 as a primary 'vortical flow40. Suitable fuel delivery means 42 are provided to deliver fuel to theinterior of the housing 35 as will presently be explained. The fueldelivery means 42 may comprise a conduit 44, having a discharge end 45,which extends through the outer shell 20 and communioates with a sourceof pressurized fuel (not shown). While the improved fuel deliveryapparatus 34 is particularly adapted for use with liquid fuel and willhereinafter be described in connection 'with liquid fuel, it should beunderstood that fuel in the liquid state, gaseous state, solid state ora combination thereof may be effectively used.

Referring now to FIGS. 2-4, the housing 35 has been shown to comprise aninvolute outer wall 48 and generally planar, spaced upstream anddownstream end walls 50 and 52, respectively, which are peripherallyjoined to the outer wall 48. As best shown in FIG. 3, the housing 35defines an air vortex generator or spin chamber 46 out wardly of theoutlet 38. The outer wall 48 is of spiral shape with a progressivelydecreasing radius from the inlet passage 36 to a terminal edge or lip 54(FIG. 2) which defines, in part, the inlet opening from passage 36 tothe spin chamber 46. The inlet passage 36 is formed with a generallyaxially facing upstream end opening 55 for receiving a flow ofpressurized air from compressor 28 and has one wall formed as astreamline continuation of the involute outer wall 48 so as to deliverthe inlet air in a 4 generally streamline manner into the spin chamber46. In this manner, the pressurized inlet air is directed from inlet 36in a circular motion of ever decreasing radius so as to generate theprimary vortical flow 40' as shown in FIG. 1. As schematically shown inFIG. 3, the vortex has a substantially hollow core portion 56.

To further provide the swirling motion of the primary vortical flow 40as well as to accurately position the vortical flow 40 relative to theopening 38, a plurality of primary swirl vanes 58, each of which extendsbetween the upstream and downstream walls and 52, may be provided in aperipheral array about the outlet 38 as shown in FIG. 2. Such an arrayof swirl vanes 58 may also be adapted to throttle the air passingtherethrough so as to increase the rotational velocity of the primaryvortical flow 40. In order to maintain a generaly uniform rotationalvelocity of the inlet air within the spin chamber 46, outwardly of thevanes 58, the outlet 38 and the swirl vanes 58 are preferably positionedwith respect to the outer wall 48 so that the cross-sectional flow areaprogressively decreases from the inlet to the lip 54.

In addition to the primary flow generating apparatus just described, acontrol or collector surface 60 is provided at the outlet 38 to collectdownstream wall fuel flow as will be described. The collector surface 60cooperates with means 62 for introducing a secondary flow of air intosaid combustion chamber 14 about and along the collector surface 60 in amanner which carries such collected fuel as an atomized spray into thecombustion chamber 14. In the depicted embodiment, the control orcollection surface 60 takes the form of an annular sleeve extendingaround the outlet 38 and defining a downstream extension thereof. Thecollection surface 60 may be suitably joined to the downstream wall 52or formed integrally therewith. The secondary air flow means 62 has beenshown as comprising a plurality of swirl vanes 64, spaced radiallyoutwardly of and in a circular array around, sleeve 60. The swirl vanes64 are suitably secured between the downstream wall 52 and an annularrim 65 spaced axially downstream thereof. The array of swirl vanes 64and the annular rim 65 are spaced radially outwardly of the sleeve 60 soas to form an axially extending annular passage 66 therebetween which isgenerally coaxial with the outlet 38 and with vortical flow 40.

As best shown in FIG. 1, the fuel injection apparatus 34 is positionedwith the annular rim closely spaced or joined to the rim of enclosuremember opening 18 so as to establish a flow of pressurized air fromchamber 33, radially inwardly through the swirl vanes 64, and henceaxially into the combustion chamber 14. The swirl vanes 64 are adaptedto swirl such air flow and generate a secondary vortical flow 67 whichis preferably counterrotating relative to the primary vortex flow 40,although it may be otherwise. In this manner, a region of high shearstress 68 is created downstream of the sleeve 60' at the outer boundaryof the vortex 40 due to the interaction of the primary and secondaryflows.

In operation, liquid fuel is delivered to inlet passage 36 through theconduit 44. Some of this fuel may be immediately picked up by orentrained within the high velocity inlet air entering through the inlet55 and carried into the combustion chamber 14. The remaining fuel landson the interior surface of the inlet passage 36 and is driven or pushedby the high velocity air to the spin chamber 46 and centrifugally alongouter wall 48. During such flow, a portion of the fuel may be vaporizedand/ or atomized and entrained within the inlet air flow. A portion ofthe outer wall fuel flow which is not so evaporated is then sheared offthe lip 54, as at 72 (FIG. 2), and again passes through the inlet airfiow pathwhich results in more fuel being entrained within the inletair. In addition to the above and with reference to FIG. 3, the liquidfuel circulating within spin chamber 46 is carried by the air in aswirling flow along the inner surface of upstream wall '50 by theswirling air flow. Such upstream wall fuel flow is carried through thevanes 58 and forms a ring of fuel 74 where the fuel velocity forces arebalanced by the centrifugal forces. While flowing along the innersurface of upstream wall 50 to the ring 74, some of the fuel may beevaporated from the surface by the inlet air and by radiant heat fromthe flame within the combustion chamber '14. The liquid fuel within thering of fuel 74 is spun off and atomized into extremely small fueldroplets by the high velocity vortical flow of air 40 and directed orcarried toward the combustion chamber 14 as a conical spray 76. Sincethese atomized fuel droplets are extremely small, they quickly vaporizeand mix with the air vortex 40.

Any fuel flow along the downstream wall 52 is carried or pushed to thedownstream end of the sleeve 60 in a swirling flow by the vortex 40. Thefuel is then spun or sheared 01f the downstream end of the sleeve 60 bythe primary and secondary flows 40 and 67 and carried into the region 68of high shear stress where it is sheared to small droplets 80 whichquickly vaporize. Accordingly, by providing the control surface orsleeve 60 and the secondary flow generating means 62, positive andcontrolled introduction of all liquid fuel efiluxing from the apparatus34 is achieved over a wide range of operating conditions in a gasturbine engine.

Referring again to FIG. 3, the reduced pressure of the vortex core 56causes a reverse or recirculation flow to be established from thecombustion chamber 14, as generally shown at 82. This recirculation ofhigh temperature gas from the combustion chamber .14 into the central orcore portion of the spin chamber 46 further enhances vaporization of theliquid fuel from the spin chamber surfaces as well as vaporization ofany atomized fuel droplets carried by the air intake or expelled fromthe fuel ring 74. This recirculation of high temperature gas, however,can have detrimental effects if it is permitted to impinge upon theupstream wall 50 of the spin chamber 46'. That is, the impingement ofthe high temperature air can cause an overtemperature of the wall 50with resultant damage thereto. Additionally, the impingement can resultin the accumulation of carbon deposits on the wall 50, as shownschematically by the numeral 84. Such accumulation interferes with thenormal operation of the apparatus 34 thereby causing unpredictableburning conditions in the combustion chamber 14. An additional problemresults when the carbon accumulation 84 breaks loose from the upstreamwall 50 and travels downstream through the combustion chamber 14.Therefore, some means is necessary to prevent the impingement of therecirculating high temperature gases 82 upon the upstream wall 50 toprevent the overtemperature and carbon accumulation problems.

One possible approach to this problem might be to perforate the upstreamwall 50 and to pass copious amounts of high velocity air therethrough,thus preventing impingement by the hot recirculating gases 82. Such anapproach, however, frequently destroys the basic aerodynamics of thesystem by upsetting the primary vortex 40. The net result of such asystem is a worsening of ignition capability and poorer fueldistribution, thereby causing poorer temperature distribution withresultant turbine damage.

To eliminate this problem, as shown in FIG. 4, the upstream wall 50 isprovided with an opening 86 centrally thereof. A pan-shaped cover 88 isplaced over the opening 86 and is attached to the upstream wall 50 byany appropriate means such as by welding. The cover 88 is provided witha plurality of small holes 90 appropriately spaced circumferentiallyaround the flat plate portion of the cover 88. The holes 90 may beinclined with respect to the flat plate portion of the cover 88 as shownin FIG. 5. As shown in FIG. 1, the cover 88 is located within thechamber 33 such that high velocity air entering the chamber 33 throughthe opening 32 is capable of flowing through the holes '90 to aninterior chamber 92 (FIG. 4) formed between the cover 88 and the wall50. The chamber 92 lies in fluidic flow cooperation with the spinchamber 46 by means of the opening 86. Air entering the holes 90 thusflows through the chamber 92 into the spin chamber 46 as purge airschematically shown by the arrows 94. As shown in FIGS. 4 and 5,however, the holes 90 are positioned to prevent direct axial flowbetween the holes 90 and the central opening 86 of the forward wall 50.Additionally, the holes 90 are inclined as shown in FIG. 5 so that thepurge air swirls 'within the chamber 92 prior to exiting through theopening 86. The holes 90 are preferably inclined in a direction toprovide swirling motion in the same direction as the primary vortex flow40.

The holes 90 are appropriately spaced and sized to regulate the amountand the pressure of the purge air 94 flowing into the chamber 46 inorder to prevent high velocity air flow from destroying the primaryvortex 40. As shown in FIG. 4, the purge air 94 entering the opening 86is made to turn over the forward wall 50 along the interior surfacethereof by the pumping action of the vortex 40, aided by its ownswirling motion as described above. This air flow exits at a low enoughvelocity such that the aerodynamics of the spin chamber 46 are notdestroyed, but it enters at a high enough velocity such that therecirculating hot gases 82 never impinge upon the upstream wall 50 ofthe spin chamber 46. Thus, carbon is prevented from depositing upon theupstream wall 50, the upstream wall 50 is maintained cool, and theoverall performance of the combustion apparatus 34 is not sacrificed.

From the foregoing, it will be appreciated that the present inventionprovides an improved combustion apparatus of simplified and economicalconstruction for ef ficiently and satisfactorily introducing fuel into acombustion chamber in a positive and controlled manner over a wide rangeof operating conditions while preventing carbon accumulation and metalovertemperature of such apparatus. While the purge air inlet means havebeen shown and described as comprising a pan-shaped member including aplurality of small holes located therein, it should be understood thatother arrangements may be employed and that such means may be formedintegrally with the apparatus 34. Additionally, while a plurality ofsmall purge holes have been shown, one larger hole could be utilized ifappropriately positioned within the cover 88. Accordingly, while apreferred embodiment of the present invention has been depicted anddescribed, it

will be appreciated by those skilled in the art that many Imodifications, substitutions, and changes may be made thereto withoutdeparting from the inventions fundamental scheme.

What is new and desired to be secured by Letters Patent of the UnitedStates is:

1. In a combustion apparatus of the type including a hollow bodydefining a combustion chamber therein, means disposed outwardly of saidcombustion chamber for defining a spin chamber including upstream anddownstream end walls, said spin chamber including means adapted toreceive pressurized air and liquid fuel and to circulate said air andsaid fuel about a centrally disposed outlet in said downstream wall ofsaid spin chamber and to generate a primary vortical discharge flow ofsaid air and said fuel from said outlet into said combustion chamber,and means for igniting said discharge flow to form a high temperaturegas stream, the improvement which comprises:

an opening formed in said upstream end wall of said spin chamber, meansforming a purge air chamber adjacent said opening, and means forgenerating a flow of purge air through said opening into said spinchamber, along said upstream end wall, to prevent impingement of thehigh temperature gas stream upon said upstream end wall.

2. The improved apparatus of claim 1 further characterized in that saidopening is located centrally of said upstream end wall, said chamberforming means comprises a pan-shaped member, and said pan-shaped membercovers said opening and includes at least one purge air hole formedtherein.

3. The improved apparatus of claim 2 further characterized in that saidpan-shaped member includes a plurality of purge air holes formedtherein, said purge air holes being located radially outwardly of saidcentral opening, thereby preventing direct axial flow of purge air intosaid spin chamber.

4. The improved apparatus recited in claim 3 further characterized inthat said purge air holes are inclined with respect to said pan-shapedmember, whereby said purge air is provided with a swirling motion withinsaid purge air chamber.

5. The improved apparatus of claim 2 further comprising means forming acontrol surface around said outlet for collecting liquid fuel flowingalong said downstream wall to said outlet, and means for generating asecondary flow of air into said combustion chamber, about said fuelcollection means, to form a region of high shear stress at the outerboundary of said primary vortical flow, whereby said collected fuel isintroduced into said combustion chamber in a controlled and highlydispersed manner.

6. The improved apparatus of claim 5 further characterized in that saidfuel collection means comprises an annular sleeve generally coaxiallydisposed relative to said primary vortical flow, said sleeve beingsecured to said downstream end wall about said outlet.

7. The improved apparatus of claim 6 further characterized in that saidsecondary flow generating means includes a plurality of swirl vanesdisposed in a radially outwardly spaced circular array about saidannular sleeve, said swirl vanes being adapted to deliver said secondaryflow as a vortex about, and counterrotating relative to, said primaryvortical discharge flow.

8. Apparatus for introducing fuel into a combustion chamber to beignited to form a high temperature gas stream, said apparatuscomprising:

a housing having upstream and downstream end walls, said downstream endwall including a core outlet therein, said housing defining a spinchamber around said core outlet, said core outlet including means toestablish flow communication between said spin chamber and saidcombustion chamber;

means for receiving anddirecting pressurized air and fuel into said spinchamber;

said spin chamber including means to utilize the energy in flowcommunication with said spin chamber; and

means for generating a flow of purge air through said opening, saidpurge air flowing along said upstream end wall and preventing theimpingement of the high temperature gas stream thereon.

9. Apparatus as described in claim 8 further characterized in that saidpurge air chamber forming means comprises a pan-shaped member, saidpan-shaped member covering said opening and including a plurality ofpurge air inlet holes forced therein.

10. The apparatus recited in claim 9 further characterized in that saidpurge air inlet holes are disposed radially outwardly of said opening,thereby preventing direct axial flow of purge air into said spinchamber, and are inclined with respect to said pan-shaped member,whereby purge air flowing within said purge air chamber is given aswirling motion.

11. The apparatus recited in claim 9 further comprising means carried bysaid downstream end wall for defining an axially downstream extendingfuel collection surface, said collection surface defining said coreoutlet at its junction with said downstream end wall; and means fordirecting a secondary flow of pressurized air into said combustionchamber, about said collection surface, so as to form a region of highshear stress at the outer boundary of said primary vortical flow,whereby fuel collected on said collection surface is discharged in acontrolled and highly dispersed manner.

References Cited UNITED STATES PATENTS 2,560,207 7/1951 Berggren et al-3965 2,807,316 9/1957 Jackson 6039.65X 3,030,773 4/1962 Johnson 6039.653,405,923 10/1968 Nesbitt et a1. 43 l-l83X ALLAN D. HERRMANN, PrimaryExaminer US. Cl. X.R.

